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We present a detailed experimental investigation which uncovers the nature of light bullets generated from self-focusing in a bulk dielectric medium with Kerr nonlinearity in the anomalous group velocity dispersion regime. By high dynamic range measurements of three-dimensional intensity profiles, we demonstrate that the light bullets consist of a sharply localized high-intensity core, which carries the self-compressed pulse and contains approximately 25% of the total energy, and a ring-shaped spatiotemporal periphery. Subdiffractive propagation along with dispersive broadening of the light bullets in free space after they exit the nonlinear medium indicate a strong space-time coupling within the bullet. This finding is confirmed by measurements of a spatiotemporal energy density flux that exhibits the same features as a stationary, polychromatic Bessel beam, thus highlighting the nature of the light bullets.

We report on the generation of ultrabroadband supercontinuum (SC) by filamentation of two optical-cycle, carrier-envelope phase-stable pulses at 2 μm in fused silica, sapphire, CaF₂ and YAG. The SC spectra extend from 450 nm to more than 2500 nm, and their particular shapes depend on dispersive properties of the materials. Prior to spectral super-broadening, we observe third-harmonic generation, which occurs in the condition of large phase and group velocity mismatch and consists of free and driven components. A double-peaked third-harmonic structure coexists with the SC pulse as demonstrated by the numerical simulations and verified experimentally. The SC pulses have stable carrier envelope phase with short-term rms fluctuations of ∼ 300 mrad, as simultaneously measured in YAG crystal by f-2f and f-3f interferometry, where the latter makes use of intrinsic third-harmonic generation.

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We exploit inverse Raman scattering and solvated electron absorption to perform a quantitative characterization of the energy loss and ionization dynamics in water with tightly focused near-infrared femtosecond pulses. A comparison between experimental data and numerical simulations suggests that the ionization energy of water is 8 eV, rather than the commonly used value of 6.5 eV. We also introduce an equation for the Raman gain valid for ultra-short pulses that validates our experimental procedure.Keywords: Inverse Raman Scattering, light matter interaction, cold plasma Femtosecond laser pulses tightly focused in dielectric media have a wide range of applications in science and technology. Because of their capability to deposit high ionization doses in volumes of a few cubic microns, they can be used to induce permanent, microscopic refractive index modification in solid dielectrics, thus enabling three-dimensional integrated optics 1,2 . By focusing femtosecond pulses in liquids, it is possible to induce localized chemical reactions such as photo-polymerization on the micro-nano-scale 3 . In aqueous media, such as biological tissues, tightly focused femtosecond laser pulses have been successfully employed for eye surgery 4 and treatment of cancerous cells 5 . Recent studies show that by tuning the input pulse chirp an effective control on the energy deposition in water is reached 6 . Future developments of these applications will benefit from a more advanced control of the energy deposition by means of arbitrarily spatiotemporally tailored laser wavepackets 7 . In this context, suitable diagnostic tools for real time analysis of energy deposition dynamics as well as a better understanding of the initial stages of the energy absorption in the dielectric medium are of foremost importance.In previous experiments based on quantitative shadowgraphy, we characterized the propagation of a 120 fs pulse focused with low NA in water 8,9 . In this configuration, the laser pulse enters a filamentation regime 10 leaving behind a tenuous, few-mm-long plasma channel which gets solvated on a ps timescale. The pulse dynamics (featuring pulse splitting and superluminal pulse formation) was clearly seen in the probe as an absorption feature, which we attributed to the imaginary part of an unspecified cross-phase modulation process (XPM) between pump and probe. a) Electronic mail: stefano@stefanominardi.eu.; http://stefanominardi.eu.

International audienceWe present measurements fully characterizing the whole life cycle of femtosecond pulses undergoing filamentation in water at 400 nm. The complete pulse dynamics is monitored by means of a four-dimensional mapping technique for the intensity distribution I(x,y,z,t) during the nonlinear interaction. Measured events (focusing or defocusing cycles, pulse splitting and replenishment, supercontinuum generation, conical emission, nonlinear absorption peaks) are mutually connected.The filament evolution from laser energy deposition in water, which is of paramount importance for a wide range of technological and medical applications, is interpreted in light of simulation results

We present experimental and numerical investigations of optical extreme (rogue) event statistics recorded in the regime of femtosecond pulse filamentation in water. In the spectral domain, the extreme events manifest themselves as either large or small extremes of the spectral intensity, justified by right-or left-tailed statistical distributions, respectively. In the time domain, the observed extreme events are associated with pulse splitting and energy redistribution in space and therefore are exquisitely linked to three-dimensional, spatiotemporal dynamics and formation of the X waves.Rogue or freak waves are well known in hydrodynamics and refer to statistically rare giant waves that occur on the surface of oceans and seas (see, e.g., [1] for a review). From a general point of view, rogue waves or, more generally, rogue (extreme) events represent an extreme sensitivity of the nonlinear system to the initial conditions. Indeed, recently rogue-wave-like behavior was shown to be inherent to diverse nonlinear physical environments: propagation of acoustic waves in superfluid helium [2], variation of local atomic density in Bose-Einstein condensates [3], ion-acoustic and Alfvén wave propagation in plasmas [4], and propagation of acoustic-gravity waves in the atmosphere [5].Optical rogue waves, recently discovered by Solli et al.[6], constitute a fascinating topic in modern nonlinear optics [7,8]. At present, most of the knowledge on optical rogue waves is brought by the studies of the supercontinuum generation in optical fibers, under a variety of operating conditions and propagation regimes ranging from CW to femtosecond pulses [9][10][11][12][13][14][15], and has been shown to share a great similarity with the waves' hydrodynamical counterparts [16]. In fibers, rogue waves represent rare soliton pulses, whose statistics are characterized by extreme-value (non-Gaussian or, more specifically, L-shaped) distributions. It is generally accepted that optical rogue waves emerge as a result of the nonlinear wave interactions and soliton collisions, although the precise underlying physical mechanisms leading to their formation are still under debate [17].Extreme-value statistics are also inherent to various nonlinear optical systems, where dimensionality and nonlinear wave dynamics are more complex compared to optical fibers: nonlinear optical cavities [18], nonlinear optical lattices [19], nonlinear waveguides [20], and ultrashort pulse filamentation [21]. Ultrashort pulse filamentation is of particular interest, since it represents an ultimate regime of light and matter interaction, and the nonlinear dynamics is governed by the interplay of self-focusing and self-phase modulation, whitelight continuum generation, diffraction, nonlinear absorption, free-electron plasma generation, and space-time effects [22]. On the other hand, filamentation phenomena find a broad spectrum of applications, ranging from atmospheric analysis * Corresponding author: audrius.dubietis@ff.vu.lt[23] to laser micromachining [24], and therefore ...

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